Demo content import (and, as a side effect, opening the Brizy editor on the same request path) fails with an uncaught fatal error

# Bug report: Fatal error "Cannot call constructor" in `import/importer.php` (PHP 8.1+)

## Summary

Demo content import (and, as a side effect, opening the Brizy editor on the same request path) fails with an uncaught fatal error:

```
PHP Fatal error:  Uncaught Error: Cannot call constructor in
/wp-content/plugins/brizy/import/importer.php:39
```

Root cause: `Brizy_Import_Importer::__construct()` unconditionally calls `parent::__construct()`, but the `WP_Importer` base class it extends (loaded from WordPress core's `wp-admin/includes/class-wp-importer.php`) defines **no constructor at all** — not even a legacy PHP4-style one. Calling `parent::__construct()` when no class in the inheritance chain defines that method is a fatal error in PHP on every version (this is not a PHP-8.3-specific removal); it simply hadn't been noticed because most installs don't exercise this code path, or happen to have another plugin/mu-plugin defining `WP_Importer` with a constructor before Brizy's own conditional `require`.

## Environment

- Brizy (free): **2.8.22**
- Brizy Pro: **2.8.12**
- PHP: **8.3.32** (64-bit), SAPI `apache2handler`
- Web server: Apache/2.4.52
- OS: Linux 6.8.0-136-generic x86_64
- OPcache: enabled
- Host: shared hosting (Timeweb)
- WordPress core's `wp-admin/includes/class-wp-importer.php` on this install carries the `#[AllowDynamicProperties]` attribute (added to WP core in 6.1), for reference — no constructor is defined anywhere in that file.
- Other active plugins at time of failure: Akismet, Cyr-To-Lat, Yoast SEO, WP File Manager, Yandex Metrika (no third-party plugin defines `WP_Importer` on this install, so Brizy's own `require ABSPATH . 'wp-admin/includes/class-wp-importer.php'` fallback is what runs).

## Steps to reproduce

1. Fresh/clean WordPress + Brizy + Brizy Pro install, PHP 8.3.
2. Trigger the demo content importer (`wp_ajax_brizy-import-demo` → `Brizy_Import_Main->ajaxImportDemo()`).
3. Import fails immediately with the fatal error below. The editor also errors out on the same/related pages until the import completes successfully.

## Error log

```
[PHP Deprecated] Function libxml_disable_entity_loader() is deprecated in
  .../wp-content/plugins/brizy/import/parsers/simplexml.php on line 18
[PHP Deprecated] Function libxml_disable_entity_loader() is deprecated in
  .../wp-content/plugins/brizy/import/parsers/simplexml.php on line 22
[PHP Fatal error]  Uncaught Error: Cannot call constructor in
  .../wp-content/plugins/brizy/import/importer.php:39
Stack trace:
#0 .../wp-content/plugins/brizy/import/import.php(44): Brizy_Import_Importer->__construct(Array, Object(Brizy_Import_Extractor))
#1 .../wp-content/plugins/brizy/import/main.php(121): Brizy_Import_Import->import(false)
#2 .../wp-includes/class-wp-hook.php(353): Brizy_Import_Main->ajaxImportDemo('')
#3 .../wp-includes/class-wp-hook.php(377): WP_Hook->apply_filters('', Array)
#4 .../wp-includes/plugin.php(523): WP_Hook->do_action(Array)
#5 .../wp-admin/admin-ajax.php(192): do_action('wp_ajax_brizy-i...')
#6 {main}
  thrown in .../wp-content/plugins/brizy/import/importer.php on line 39
```

## Relevant source (current trunk, `import/importer.php`)

```php
if ( ! class_exists( 'WP_Importer' ) ) {
    $class_wp_importer = ABSPATH . 'wp-admin/includes/class-wp-importer.php';
    if ( file_exists( $class_wp_importer ) ) {
        require $class_wp_importer;
    }
}

class Brizy_Import_Importer extends WP_Importer {
    ...
    public function __construct( $data, $extractor ) {
        if ( ! function_exists( 'post_exists' ) ) {
            require_once ABSPATH . 'wp-admin/includes/post.php';
        }

        parent::__construct();   // <-- line 39, fatals: WP_Importer has no __construct()
        ...
    }
}
```

I confirmed the mechanism in isolation on plain PHP 8.4 as well — calling `parent::__construct()` when no ancestor class defines `__construct()` always throws `Error: Cannot call constructor`, independent of the PHP version. Since WP core's `WP_Importer` never defines a constructor, this line only "works" on installs where something else has already defined a different `WP_Importer` class (with a real constructor) before Brizy's own `require` runs.

## Suggested fix

Guard the call, since `WP_Importer` has nothing to construct:

```php
if ( method_exists( 'WP_Importer', '__construct' ) ) {
    parent::__construct();
}
```

or simply remove the `parent::__construct();` call — it is a no-op today for the WP-core `WP_Importer`.

## Workaround applied on our end

We patched line 39 of `wp-content/plugins/brizy/import/importer.php` with the guarded version above so the client's site is unblocked. Flagging this so it can be fixed upstream — otherwise the patch will be lost on the next Brizy update, and other users hitting the demo importer on stock WordPress installs (without a third-party `WP_Importer`) will keep hitting this fatal.

Happy to provide further details (full `wp_debug.log`, `phpinfo()`, etc.) if useful.